Because the demand for oil and gas continues to grow, safer and more reliable methods of developing oil and gas fields need to be developed. Producing gas from the Arctic Ocean provides unique challenges, especially as drilling moves into deeper water depths, faces more severe ice conditions, and as well complexity increases.
Ice floe detection has been developed using a variety of ice monitoring systems. Strass (1998) derives ice draft and coverage from acoustic measurements made with moored UPWARD LOOKING Sonar's (ULS') sounding the sea surface remotely from below. Harms, et al., (2001) use moored ULS data to measure sea ice draft. Wadhams, et al. (2006) developed an autonomous underwater vehicle (AUV) for under-ice studies with an unmanned under-ice vehicle and a multibeam sonar. Hyatt, et al. (2008) use upward-looking acoustic Doppler current profiler (ADCP) to determine ice coverage with moored systems. (Theriaul, et al., 2009).
Johnson, GB2223642, describes methods of tracking the movement of sea-ice using successive images from orbiting satellites. Deines and Maier, U.S. Pat. No. 5,122,990, indicate that a signal echo may be used in an upward looking configuration to measure the movement of sheets of ice in one of the Polar Regions. Glynn, et al., U.S. Pat. No. 5,381,694, provides a relatively inexpensive reflectometer apparatus that can measure the thickness of material such as ice. Yankielun and Ferrick, U.S. Pat. No. 5,585,799, pertains to a microwave continuous wave (CW) Doppler radar system for river ice motion detection and real-time kinematic data acquisition using digital signal processing equipment. Matsuoka, et al., U.S. Pat. No. 7,095,359, describe an ice thickness/drifting velocity observation of sea ice by using an ice thickness measurement sonar and a current meter moored into the sea and a sea ice observation by a high-resolution airborne SAR are synchronously performed to calculate a correlation between a draft profile of sea ice passing over the sonar and an SAR backscattering coefficient profile. Williams and Yankielun, U.S. Pat. No. 6,700,528, provide a compact and relatively inexpensive motion detection and alerting system implemented in a single, environmentally secure and benign package. Although a variety of ice floe monitoring equipment has been developed, these systems are limited to small areas, fixed positions within the ocean or near the equipment, or limited in the amount of time available.
Oil and gas companies wishing to drill and develop an oil or gas field in the offshore Arctic Ocean need to know on a near continuous basis what kind of ice environment they are dealing with. In the Alaska and Beaufort Canadian areas of the Arctic Ocean, the ice is usually composed of “floes”, large bodies of ice that may extend up to several hundred square miles in area and 100 feet in thickness. These floes move around in a somewhat erratic and unpredictable fashion. Although satellite imaging can be used to track ice floes on a near-continuous basis and predict with certain probabilities where they are heading, as well as measuring their area in the x and the y direction (FIG. 1), the third dimension, the thickness of the ice floe, cannot be measured satisfactorily. What is required is a method to measure and monitor on a continuous basis large areas of the ice floes including details of the under-ice topography, in particular the thickness of the ice.
Thick regions of ice can be created when floes collide and overlap or stack, or alternatively by so-called multi-year ice, that is to say floes which endure year on year and whose thickness accumulates over the years. The former sort is less dangerous, being generally weaker and easier to break up; the latter sort tends to be stronger and therefore more dangerous.